Blood lead levels measured prospectively and risk of spontaneous abortion

Studies of low to moderate level lead exposures have reported mixed finding s regarding the risk of spontaneous abortion, despite lead's abortifacient properties at very high doses. To evaluate the risk of spontaneous abortion from low or moderate lead exposures, a nested case-control study was condu cted within a cohort of pregnant women in Mexico City, 1994-1996, During th eir first trimester, 668 women enrolled, were interviewed, and contributed blood specimens. Pregnancies were followed by home visits or telephone call s. Spontaneous abortions before week 21 (n = 35) were matched with pregnanc ies that survived beyond week 20 (n = 60) on maternal age, hospital, date o f enrollment, and gestational age at enrollment. Mean blood lead levels wer e 12.03 mu g/dL for cases and 10.09 mu g/dL for controls (p = 0.02), Odds r atios for spontaneous abortion comparing 5-9, 10-14, and greater than or eq ual to 15 mu g/dL with the referent category of <5 mu g/dL of blood lead we re 2.3, 5.4, and 12.2, respectively, demonstrating a significant trend (p = 0.03), After multivariate adjustment, the odds ratio for spontaneous abort ion was 1.8 (95% confidence interval = 1.1, 3.1) for every 5 mu g/dL increa se in blood lead. Low to moderate lead exposures may increase the risk for spontaneous abortion at exposures comparable to US general population level s during the 1970s and to many populations worldwide today; these are far l ower than exposures encountered in some occupations.